Satellite-based navigation systems such as the Global Positioning System (GPS) may suffer degradation and outages due to multipath reflectors and blockages between the satellite transmitters and the vehicle's GPS antenna. This results in degraded performance, particularly in urban canyons and tunnels. To provide navigation updates in the absence of GPS signal reception, a variety of dead reckoning enhancements have been offered as adjuncts to GPS navigation systems. Navigation using dead reckoning involves calculating a current position based upon the heading and distance from a previously known position. Dead-reckoning sensors provide information such as vehicle velocity, acceleration, heading, etc. to aid a GPS receiver in its navigation solution. Typical sensors include the vehicle odometer, individual wheel speed sensors, rate gyros, accelerometers, magnetic compass, and barometric pressure sensors. Many of these sensors incur the costs of either a) purchasing the additional sensors and integrating them with the navigation system, or b) getting access to existing sensor data on a vehicle data bus, which can raise vehicle safety and warranty issues. As such, the cost of acquiring specialized sensors and/or the complication of integrating such sensors into a satellite-based navigation system have prevented widespread adoption of dead-reckoning sensors into vehicle navigation system using GPS.
Accordingly, there is a need in the art for improved satellite-based navigation systems that can practice dead reckoning as an adjunct navigation technique without requiring additional or difficult-to-integrate dead-reckoning sensors.